Earlier this year, Warren co-signed a letter with other Senate Democratic women urging the former first lady, senator and secretary of state to run in 2016. But she sidestepped a direct question from the New Republic's Noam Scheiber about the possibility of taking on Clinton in 2016.

“You’ve asked me about the politics,” Warren said. “All I can do is take you back to the principle part of this. ... I know what I am in Washington to do: I’m here to fight for hard-working families.”

Most insiders say Clinton would be an overwhelming favorite against any Democratic primary opponent. One far-too-early poll released in July showed Clinton holds a 48-point lead over Vice President Joe Biden and a 50-point advantage over Warren among Iowa Democrats.

However, former aides say the former Harvard law professor would be undeterred by polls.

“She has an immense — I can’t put it in words — a sense of destiny,” one said. “If Hillary or the man on the moon is not representing her stuff and her people don’t have a seat at table, she’ll do what she can to make sure it’s represented.”

Scheiber lays out Clinton's "nightmare" like this:

Any candidate who challenged Clinton would need several key assets. The candidate would almost certainly have to be a woman, given Democrats’ desire to make history again. She would have to amass huge piles of money with relatively little effort. Above all, she would have to awaken in Democratic voters an almost evangelical passion. As it happens, there is precisely such a person. Her name is Elizabeth Warren.

Reminder: The first votes that count in the 2016 presidential campaign, the Iowa caucuses, are scheduled for early January 2016.